feat: migrate ESLint to v9 flat config

- Replace .eslintrc.json with eslint.config.mjs
- Simplify configuration using @antfu/eslint-config
- Add necessary ESLint plugin dependencies
- Disable overly strict style rules
- Set package.json type to module for ESM support
- Fix ESLint disable comment format

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

i18n/client.ts

@@ -12,6 +12,5 @@ export const getLocaleOnClient = (): Locale => {
 export const setLocaleOnClient = (locale: Locale, notReload?: boolean) => {
   Cookies.set(LOCALE_COOKIE_NAME, locale)
   changeLanguage(locale)
-  if (!notReload)
-    location.reload()
+  if (!notReload) { location.reload() }
 }